David Cameron this morning. 'Every time a minister announces a clampdown on access to benefits … they also chip away at the delicate tissue of mutual obligation that sustains social cohesion.' Photograph: Matt Dunham/AP

But that's all it is. That is what the EU commissioner László Andor tried to point out when he suggested a fact-based debate would be a good thing, a debate that acknowledged, for example, that it is the obligation of the new migrant's native country to pay unemployment benefit.

Debate about migration, however, doesn't take place at any rational level. It is the most emotive issue in politics today, and every policy initiative makes that emotional response more rational. People's attitudes to it can be quite accurately predicted – as OECD research shows – by income and class. After all, most of us want to be confident that we have access to a reasonable level of state support if we need it, and we're happy to pay for it even though it makes a painful hole in the household accounts.

And it is very easy to allow people to believe that there are others – maybe even their neighbours – who are taking out but aren't paying in. It's a breach of the very basic code of fairness.

Not that there is any evidence that new migrants are doing that. But then, there's very little good evidence about migration and migrant activity at all. Most people think of migrants as a single homogenous group. Few distinguish between people from the Asian subcontinent, who may be coming to study or to join family; or from Nigeria (the two biggest non-EU migrant groups into the UK). It is rarely mentioned (though I may have, several times) that EU migrants in particular are young, fit and on the whole well educated. They are less likely to rely on benefits than other groups, at least until they form families. It is almost never explained that there are several different ways of measuring immigration – none of which, as MPs pointed out in the summer, is very reliable. One of the EU commission's complaints about the UK is a tendency to make assertions about benefit tourism without producing the evidence to back them up.

Now migration policy is locked into a dangerous bidding war that makes it harder than ever to question the underlying assumptions, to try to establish the facts and to get a counter-argument out into the public space. Recognising that people often feel rather than think about migration is not to deny that concern about strains on public services and anxiety about housing shortages and pressure on schools and hospitals, are all entirely legitimate. But the more politicians announce policy changes and promise impossible targets (such as the Tory pre-election pledge to cut net migration by more than half), the more voters feel frustrated and mistrustful. Politicians in turn step up the rhetoric. And that is where the real danger lies.

Every time a minister announces a clampdown on access to benefits, or a zero-tolerance attitude to vagrancy – which in Cameron's article this morning is undoubtedly meant to be read as "Go home, Roma" – they also chip away at the delicate tissue of mutual obligation that sustains social cohesion. Every time politicians try to persuade voters that they are protecting the mutuality that is conferred by citizenship and a national identity by defining non-members and denying them access, they are in fact damaging it. But they've set this vicious circle spinning and now there's no easy way off it.